A heating system by use of a heater core for a hybrid vehicle is known in the art, according to which heat exchange is carried out between engine cooling water and air to be blown into a passenger compartment of the vehicle. For example, as disclosed in Japanese Patent Publication No. 2006-152827, when an engine operation is turned on in order to carry out an air-conditioning operation, an engine is operated in a load operating mode in which a battery charging operation is also carried out. The above prior art aims at improving a fuel consumption ratio by the above engine operation.
In the vehicle control system of the above prior art, the engine is operated in the load operating mode, wherein a predetermined SOC (State Of Charge) value higher than an ordinary upper limit value of the SOC is set as an upper limit SOC value for the load operating mode in order that excess amount of generated electric power is charged in a battery as much as possible. In the load operating mode, a warm-up operation is also carried out for the engine as well as the battery. However, in a case that the SOC value is high, the amount of the generated electric power to be charged into the battery is limited. As a result, it is not always possible to carry out the engine operation of the load operating mode in which the battery charging operation is also carried out.